cell membrane- limits to cell size

Question 1

limits

Answer 1

diffusion is an effective way of moving substances into and out of cells
consequently a large SA:vol ratio is more effective

Question 2

ratios

Answer 2

as the SA:volume ratio increases, the size of the cube decreases
likewise, as a cube increases in size, its SA:vol decreases

Question 3

limitations to cell size

Answer 3

a low/small surface area to volume ratio means that diffusion is slower

a large surface area to volume ratio means that diffusion is faster

Question 4

CUBE TABLE

Answer 4

cube size | surface area | volume (hdw) | surface area
to volume ratio
2cm 2 x 2 x 6 = 242 2 x 2 x 2 = 83 24 to 8 = 3:1
3cm 3 x 3 x 6 = 542 3 x 3 x 3 =273 54 to 27 2:1
4cm 4 x 4 x 4 = 962 4 x 4 x 4 = 643 96 to 64 1.5:1
5cm 5 x 5 x 6 = 150cm2 5 x 5 x 5 =1253 150 to 125 1.2:1

Question 5

as cell size increases:

Answer 5

its volume increases at a faster rate than the surface area
there is less surface area, so the surface area to volume ratio decreases
large cells will have difficulties in exchanging materials at rates adequate to meet demands. Cell size is limited by diffusion capacity

Question 6

limitations to cell size

Answer 6

real organisms have more complex shapes but the same principles apply/ The surface area-volume relationship has important implications for processes involving transport into and out of cells across membranes

Question 7

multicellular organisms

Answer 7

to overcome the problems of small cell size, plants and animals become multicellular. They have a small surface area compared to their volume but have evolved various adapative features to increase their effective surface area (eg. respiratory gases on an elephant cannot reach body tissues by diffusion across the body surfaces alone)

Question 8

large organisms limitations to cell size

Answer 8

the surface area of an elephant is increased, for radiating body heat by large ears. Speaclised exchange surfaces (eg. lungs, skin) provide a high surface area across which exchanges with the environment can be made. Complex organ systems link exchange surfaces to move materials efficiently through the body between these exchange surface

Question 9

small organisms limitations to cell size

Answer 9

The small size of single-cell protists such as the Ameoba, provides a larger surface area relative to the cell’s volume. This is adequate for materials to be moved directly into and out of the cell by diffusion or active transport across the plasma membrane

Question 10

limitations to cell size

Answer 10

thus, there is a physical limit for the size of a cell, with the effectiveness of diffusion being the controlling factor

Question 11

limitations to cell size (large organisms)

Answer 11

as an organism becomes larger, its surface area decreases relative to its volume and diffusion ceases to be an effective way to exchange materials with the environment

Question 12

Limitations to cell size

small organisms

Answer 12

a small organism has a large surface area relative to its volume. For these organisms, diffusion is an effective way to transport materials into and out of the cell